org.apache.commons.lang3.function

Class Functions

java.lang.Object

org.apache.commons.lang3.function.Functions

public final class Functions
extends Object

Factory for Function.

Since:

3.14.0

Method Summary

Modifier and Type	Method and Description
static <T,R> R	apply(Function<T,R> function, T object) Applies the Function on the object if the function is not null.
static <T,R> R	applyNonNull(T value, Function<? super T,? extends R> mapper) Applies a value to a function if the value isn't null, otherwise the method returns null.
static <T,U,R> R	applyNonNull(T value1, Function<? super T,? extends U> mapper1, Function<? super U,? extends R> mapper2) Applies values to a chain of functions, where a null can short-circuit each step.
static <T,U,V,R> R	applyNonNull(T value1, Function<? super T,? extends U> mapper1, Function<? super U,? extends V> mapper2, Function<? super V,? extends R> mapper3) Applies values to a chain of functions, where a null can short-circuit each step.
static <T,R> Function<T,R>	function(Function<T,R> function) Starts a fluent chain like function(foo::bar).andThen(...).andThen(...).apply(...);

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

apply

public static <T,R> R apply(Function<T,R> function,
                            T object)

Applies the Function on the object if the function is not null. Otherwise, does nothing and returns null.

Type Parameters:

T - the type of the argument the function applies.

R - the type of the result the function returns.

Parameters:

function - the function to apply.

object - the object to apply the function.

Returns:

the value the function returns if the function is not null; null otherwise.

Since:

3.15.0

applyNonNull

public static <T,R> R applyNonNull(T value,
                                   Function<? super T,? extends R> mapper)

Applies a value to a function if the value isn't null, otherwise the method returns null. If the value isn't null then return the result of the applying function.

 Functions.applyNonNull("a", String::toUpperCase)  = "A"
 Functions.applyNonNull(null, String::toUpperCase) = null
 Functions.applyNonNull("a", s -> null)            = null
 

Useful when working with expressions that may return null as it allows a single-line expression without using temporary local variables or evaluating expressions twice. Provides an alternative to using Optional that is shorter and has less allocation.

Type Parameters:

T - The type of the input of this method and the function.

R - The type of the result of the function and this method.

Parameters:

value - The value to apply the function to, may be null.

mapper - The function to apply, must not be null.

Returns:

The result of the function (which may be null) or null if the input value is null.

Since:

3.19.0

See Also:

applyNonNull(Object, Function, Function), applyNonNull(Object, Function, Function, Function)

applyNonNull

public static <T,U,R> R applyNonNull(T value1,
                                     Function<? super T,? extends U> mapper1,
                                     Function<? super U,? extends R> mapper2)

Applies values to a chain of functions, where a null can short-circuit each step. A function is only applied if the previous value is not null, otherwise this method returns null.

 Functions.applyNonNull(" a ", String::toUpperCase, String::trim) = "A"
 Functions.applyNonNull(null, String::toUpperCase, String::trim)  = null
 Functions.applyNonNull(" a ", s -> null, String::trim)           = null
 Functions.applyNonNull(" a ", String::toUpperCase, s -> null)    = null
 

Useful when working with expressions that may return null as it allows a single-line expression without using temporary local variables or evaluating expressions twice. Provides an alternative to using Optional that is shorter and has less allocation.

Type Parameters:

T - The type of the input of this method and the first function.

U - The type of the result of the first function and the input to the second function.

R - The type of the result of the second function and this method.

Parameters:

value1 - The value to apply the functions to, may be null.

mapper1 - The first function to apply, must not be null.

mapper2 - The second function to apply, must not be null.

Returns:

The result of the final function (which may be null) or null if the input value or any intermediate value is null.

Since:

3.19.0

See Also:

applyNonNull(Object, Function), applyNonNull(Object, Function, Function, Function)

applyNonNull

public static <T,U,V,R> R applyNonNull(T value1,
                                       Function<? super T,? extends U> mapper1,
                                       Function<? super U,? extends V> mapper2,
                                       Function<? super V,? extends R> mapper3)

Applies values to a chain of functions, where a null can short-circuit each step. A function is only applied if the previous value is not null, otherwise this method returns null.

 Functions.applyNonNull(" abc ", String::toUpperCase, String::trim, StringUtils::reverse) = "CBA"
 Functions.applyNonNull(null, String::toUpperCase, String::trim, StringUtils::reverse)    = null
 Functions.applyNonNull(" abc ", s -> null, String::trim, StringUtils::reverse)           = null
 Functions.applyNonNull(" abc ", String::toUpperCase, s -> null, StringUtils::reverse)    = null
 Functions.applyNonNull(" abc ", String::toUpperCase, String::trim, s -> null)            = null
 

Useful when working with expressions that may return null as it allows a single-line expression without using temporary local variables or evaluating expressions twice. Provides an alternative to using Optional that is shorter and has less allocation.

Type Parameters:

T - The type of the input of this method and the first function.

U - The type of the result of the first function and the input to the second function.

V - The type of the result of the second function and the input to the third function.

R - The type of the result of the third function and this method.

Parameters:

value1 - The value to apply the first function, may be null.

mapper1 - The first function to apply, must not be null.

mapper2 - The second function to apply, must not be null.

mapper3 - The third function to apply, must not be null.

Returns:

The result of the final function (which may be null) or null if the input value or any intermediate value is null.

Since:

3.19.0

See Also:

applyNonNull(Object, Function), applyNonNull(Object, Function, Function)

function

public static <T,R> Function<T,R> function(Function<T,R> function)

Starts a fluent chain like function(foo::bar).andThen(...).andThen(...).apply(...);

Type Parameters:

T - Input type.

R - Return type.

Parameters:

function - the argument to return.

Returns:

the argument